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Even without having read the article (the site is down for me) I can say this is a wise decision. Currently the 64-bit arm cpu can also run 32-bit code. To sup

by bostand 10y ago

Even without having read the article (the site is down for me) I can say this is a wise decision. Currently the 64-bit arm cpu can also run 32-bit code. To support this it contains a 32-bit emulation layer that also exists in a few other places such as caches. By removing that, apple will be able to 1. Shrink the CPU, hence making room for more cores or bigger caches. 2. Reduce power usage by removing a significant number of gates. 3. Simplify the OS code significantly, which will probably improve performance and security.

exDM69 10y ago
Yes, it would be a smart move if they can actually drop the 32 bit mode from the CPU/SoC but I wouldn't be so sure about that. Having the 32 bit mode may still be required for the firmware/bootloader/OS early boot environment. The 32 bit mode may be partially or fully implemented using microcode and the actual silicon area that could be saved by this might not be that big. What comes to OS and firmware, yes it could be simpler but most of the code is probably there already. Getting rid of it would mean more engineering work, not less (in the short term). On the other hand, removing the parts would reduce maintenance burden in the long run. And Apple doesn't care about supporting old hardware anyway so they might as well drop it. I work with ARM SoC's but the above is no more than an educated guess as I don't know details about their CPU architecture or firmware/bootloader/OS software, take it with a grain of salt.
- nicky0 10y ago
  Presumably they can write their firmware using 64-bit code too? is there a reason it would still be 32-bit?
  - exDM69 10y ago
    If it's all their code, yes they can do it (it might be a lot of engineering, though). But it might contain 3rd party code or dependencies to something that's non trivial to port to 64 bits. If you go look at the boot procedure of a modern ARM SoC, it's pretty complex (also it's different for every SoC, there's no governing standard like the "PC is for x86"). The CPU may go through several operating modes and the procedure of booting up the cores is non-trivial. I do not think it's impossible, but the benefits for all that engineering work may not be as great as GP suggests. They are in a pretty unique position as they control all the hardware and the software, though.
    - my123 10y ago
      There is UEFI+ACPI on ARM also, that's how Windows on ARM works. Windows on ARM devices use a far more desktop-like bootchain than anything else
      - exDM69 10y ago
        Yes, but that's in addition to the dozens of proprietary boot procedures commonly used by Android tablets and smartphones and other ARM devices.
        bostand 10y ago
        Actually there are more or less only two big ones used in 2017: the well engineered open source boot solution that ARM started and is now backed by Linux and that piece of garbage that Qualcomm uses. Hopefully next year this time there will be only one.
        my123 10y ago
        UEFI with ACPI on ARM was started by Microsoft first, but is now the ARM standard :)
  - my123 10y ago
    Yes, iOS 64-bit devices use a full 64-bit bootchain

by bostand 10y ago

exDM69 10y ago

Yes, it would be a smart move if they can actually drop the 32 bit mode from the CPU/SoC but I wouldn't be so sure about that. Having the 32 bit mode may still be required for the firmware/bootloader/OS early boot environment. The 32 bit mode may be partially or fully implemented using microcode and the actual silicon area that could be saved by this might not be that big. What comes to OS and firmware, yes it could be simpler but most of the code is probably there already. Getting rid of it would mean more engineering work, not less (in the short term). On the other hand, removing the parts would reduce maintenance burden in the long run. And Apple doesn't care about supporting old hardware anyway so they might as well drop it. I work with ARM SoC's but the above is no more than an educated guess as I don't know details about their CPU architecture or firmware/bootloader/OS software, take it with a grain of salt.

nicky0 10y ago
Presumably they can write their firmware using 64-bit code too? is there a reason it would still be 32-bit?
- exDM69 10y ago
  If it's all their code, yes they can do it (it might be a lot of engineering, though). But it might contain 3rd party code or dependencies to something that's non trivial to port to 64 bits. If you go look at the boot procedure of a modern ARM SoC, it's pretty complex (also it's different for every SoC, there's no governing standard like the "PC is for x86"). The CPU may go through several operating modes and the procedure of booting up the cores is non-trivial. I do not think it's impossible, but the benefits for all that engineering work may not be as great as GP suggests. They are in a pretty unique position as they control all the hardware and the software, though.
  - my123 10y ago
    There is UEFI+ACPI on ARM also, that's how Windows on ARM works. Windows on ARM devices use a far more desktop-like bootchain than anything else
    - exDM69 10y ago
      Yes, but that's in addition to the dozens of proprietary boot procedures commonly used by Android tablets and smartphones and other ARM devices.
      - bostand 10y ago
        Actually there are more or less only two big ones used in 2017: the well engineered open source boot solution that ARM started and is now backed by Linux and that piece of garbage that Qualcomm uses. Hopefully next year this time there will be only one.
        my123 10y ago
        UEFI with ACPI on ARM was started by Microsoft first, but is now the ARM standard :)
- my123 10y ago
  Yes, iOS 64-bit devices use a full 64-bit bootchain